1. Field of the Invention
The present invention relates to an optical switch for switching-over, disconnecting, or connecting optical transmission paths. A typical example of the optical transmission path is the optical fiber. The optical fiber is superior in insulation to electrical conductor wires and not affected by electromagnetic induction, so that it has been used in various fields according as its cost lowers. Its applications have widely developed in various fields, such as, mass communications, power systems, manufacturing processes in various industrial plants for producing steel and so on, central control systems or remote monitoring control systems using a computer in traffic control systems, etc.
In these new fields, in order to more effectively use the optical fiber, a loop communication system in which optical fibers are connected in loop is employed. For example, a plurality of stations are connected in loop by a single optical fiber, and each of the stations is connected to a plurality of terminal devices by another separate fiber, so that each terminal device of one station may effect data transmission between the terminal device itself and a computer or another terminal device which are connected to another station through its associated station and the other station.
For the construction of such a system, optical switches such as listed below are needed.
(1) Optical switch for bypassing PA0 (2) Optical switch for disconnection PA0 (3) Optical switch for reforming loop PA0 (4) Optical switch for simultaneously switching-over
This switch is used for preventing the system from being inoperative in the case where an abnormal situation occurs or where diagnosis test is performed on a station, by bypassing the station so as to form a transmission loop. This bypassing optical switch is usually provided in all the stations.
This switch is used for simultaneously disconnecting all the plurality of terminal devices from their associated station for the purpose of testing the station.
This switch is used for dividing a transmission loop into two independent transmission loops, or, inversely, forming two independent transmission loops into a single transmission loop. This optical switch is effective when a disconnection fault occurs in a loop communication system and it is desired to maintain the transmission via the remaining transmission loop alone thus preventing the system operation from being stopped or shut down, or when it is desired extend the loop communication.
This switch is used for switching-over plural optical fibers, namely for not only disconnecting a plurality of optical fibers but simultaneously connecting another plurality of optical fibers.
2. Description of the Prior Art
One of the conventional optical switches is constructed such that one end of an optical fiber is attached to an end of a movable member and this movable moved is moved to one of two other opposite optical fibers, thereby switching-over the connection of the optical fibers.
Another conventional optical switch is constructed such that a triangular prism for total reflection is provided between opposed fibers and slided to switchover the connection of the optical fibers.
When these conventional optical switches are used as the optical switches (1) to (4) as mentioned above, the following necessity and problems are caused.
For the purpose of bypassing, two optical switches must essentially be installed, one at the input side of a station and the other at the output side thereof. Moreover, the station thus bypassed needs to form a self loop via another separate optical fiber therein when bypassed. This loop is used to test or diagnose the transmitting and receiving function of the station itself. In this case, still another optical switch must be provided therefor.
For the purpose of disconnecting or simultaneous switching-over, a plurality of optical switches must be incorporated and thus a problem of space is caused.
For the purpose of reforming loops, since the switch must have four change-over contacts, the switch construction becomes complicated and causes considerable light loss at the contacts.
In the optical switch, it is important that not only the construction be simple but also the number of the change-over contacts be selected as small as possible in view of the light losses caused by the contacts.
A rotary optical switching device is disclosed in the U.S. Pat. No. 3,989,943, and this device serves to only turn on or off the optical transmission paths and cannot switch the optical transmission paths.